The present disclosure relates generally to passive power filters and, more particularly, to passive LC filter components circuits such as employed in pulse-width modulated (PWM) drives and power converters.
Switched mode DC to DC converter power supplies are widely used to convert power from a source, such as mains power, to DC power supply for electronic devices. Switched mode DC to DC converters generally include buck, boost, buck-boost, fly-back, push-pull and forward converter topologies. In such cases, the DC to DC converter commonly employ large passive components for filtering of switching voltage and current ripple to provide the DC output voltage or current with ripple and noise levels within acceptable thresholds.
In some power electronic converters, resonant filters with narrow-band high attenuation (high Q) at the PWM switching frequency of the converter can be significantly smaller than the conventional low-pass filters which are generally employed for filtering noise and ripple. In order to reduce the filter loss and achieve high attenuation, the quality factor of such resonant filter tank is usually set to be high. As such, the effective bandwidth is very narrow and centered around the switching or PWM frequency. However, in fixed component based resonant filters, due to the variation of filter component values under changing operating conditions, such as varying loads or temperatures, variations of resonant tank inductance or capacitance, the high attenuation at a specific frequency cannot easily be maintained. This in turn, will cause the resonant filter to lose its high attenuation near the frequency of interest, which in turn, degrades its performance.
Accordingly, it is desirable to provide a switched mode power supply or converter output that can successfully achieve high attenuation filtering operation at a target frequency under all various changing conditions.